1. Field of the Invention
The present invention relates to an optical device module employed to a signal transmission system using light, and more particularly, to an optical device module having an improved structure of a lens installed between an optical device and an optical fiber, for focusing incident light.
2. Description of the Related Art
In general, a data transmission system using light converts an electrical signal into a light signal by a light emitting device such as a semiconductor laser and transmits the light signal to a light receiving device such as a photodetector through an optical fiber. The light receiving device converts again the light signal into an electrical signal.
In a conventional light transmission system shown in FIGS. 1 and 2, a lens 2 or 12 for focusing incident light is installed between an optical device 1 and an optical fiber 3. The optical device 1 is a light emitting device or a light receiving device. In other words, the lens 2 or 12 focuses the light emitted from the light emitting device to then be applied to the optical fiber 3, or focuses the light output from the optical fiber 3 to transmit the same to the light receiving device.
Conventionally, the lenses 2 and 12 are a ball lens shown in FIG. 1 and a gradient index (GRIN) lens shown in FIG. 2. Here, the GRIN lens 12 is a lens in which the refractive index decreases radially from an optical axis. Since the GRIN lens 12 is a plate type, it is easily adhered to the optical fiber 3 so that it is widely employed to an optical signal transmission apparatus.
In the case where the optical device 1 is a light emitting device, in order to increase a light transmission efficiency, the lens 2 or 12 is adjusted so as to align the optical axis between the optical device and the optical fiber 3.
A light receiving device employed for receiving a light signal at a high speed has a relatively small light receiving region for attaining a fast response speed. A light receiving device having an effective light receiving region of about 400 to 500 xcexcm in diameter is used in transmitting a light signal at a relatively low speed using a multi-mode optical fiber. Also, a light receiving device having an effective light receiving region of about 100 xcexcm in diameter is used in transmitting a light signal at a relatively high speed using a single-mode optical fiber.
The lenses 2 and 12 employed to optical device modules have a relatively short focal length. In particular, the ball lens 2 has light spots having noticeably different sizes according to the position of a focus.
In the case where the optical device 1 is a light receiving device, due to its small light receiving region, if the optical axis between the optical device 1 and the optical fiber 3 is off-axis or the optical device 1 is not properly positioned on the focus of the lens 2 or 12, the light emitted from the output port of the optical fiber 3 and focused by the lens 2 or 12 may be severely deviated from the effective light receiving region.
Thus, in the conventional optical device module, it is necessary to accurately adjust the optical axis for coinciding the optical axis of the lens 2 or 12 to the core center of the optical fiber 3 in order to optically couple the optical fiber 3 and the optical device 1. Also, an accurate assembly process for accurately positioning the optical device 1 on the focus of the lens 2 or 12 is required.
To solve the above problems, it is an object of the present invention to provide an optical devise module having an improved structure of a lens capable of optically coupling an optical fiber and an optical device by a simple operation for adjusting an optical axis and a simple assembly process.
Accordingly, to achieve the above object, there is provided an optical device module including an optical fiber for transmitting light, an optical device for receiving light transmitted through the optical fiber, and a lens member installed between the optical fiber and the optical device, for focusing the light emitted from the optical fiber to the optical device, the lens member having a flat plane facing the optical device and a semi-spherical convex plane facing an end of the optical fiber, and the lens member comprising a concave portion having a predetermined curvature, for transmitting incident light, formed in the center of the convex plane, a light transmitting region corresponding to the concave portion provided in the center of the flat plane, a first reflecting portion formed on the portion of the convex plane excluding the concave portion, and a second reflecting portion formed on the portion of the flat plane excluding the light transmitting region.